These devices can detect hidden bombs, weapons, and people in vehicles they pass near by, and can thus probably penetrate walls to some extent. In other words, all the controversy of Full Body Scanners have now gone mobile.

Source

Game and Story Use

I've known plenty of PCs who would love to have one of these devices to spy on the enemy. Being able to sneak peak inside a car or building could give valuable intelligence, on numbers of personnel and their armament and disposition, contraband or booby traps hidden away, etc.

The same can be turned on the PCs by various NPC factions. Big Brother is watching.

The PCs have noted the surveillance van and assume their conversations are being listened to. What they might not realize is that the full scans also reveal anything they communicate with sign language, pointing, or body language. The scanners might even reveal hidden objects and secret doors.

For more ideas, see the Full Body Scanner page. Take any of the ideas there, and put them on wheels.

Any other large technology can be likewise mounted on a vehicle, anything that's generally location-based could be mounted on wheels or even hidden in a mundane looking van. You could put a forcefield on wheels, plant a portal to the past in a porche, or travel the land in a cthulhubookmobile with fourth-dimensional altar.

And the Genius Loci of such a vehicle might eventually possess it like in Christine.

One of the Full Body Scanner vans ends up so possessed. It's a very snoopy spirit, that goes around scanning people and cars constantly. Perhaps it becomes a stalker.